A tree-lined street in Mount Pleasant
Trees: Our Allies in Climate Adaptation
A recent record-setting heatwave has broadly reinforced what many of us already knew: climate change is here. Now.
Faced with such a complex and expansive crisis, it is easy to be overwhelmed. Focusing on simple, local problem-solving can help with feelings of existential dread. So let’s shine a spotlight on a beloved and critical ally in building urban climate resilience: trees.
Trees Are Allies
Urban trees represent an elegant, multi-faceted component of natural infrastructure, and provide services well beyond carbon sinks.
Built environments such as cities retain heat and radiate it back out. This process creates what scientists call an Urban Heat Island. This heat, captured during the day, is released slowly as the sun goes down; some studies have shown that cities can be as much as 12 degrees hotter at night than nearby areas. However, trees can slow this heat absorption and provide relief from the heat through shade. Trees planted on the west and south sides of buildings are particularly effective as they shelter windows and air conditioners during the hottest times of the day, reducing energy use.
Trees also contribute to urban cooling through a process called transpiration. Water is released into the air through small pores in a tree’s leaves, literally cooling the surrounding air.
Beyond their active role as nature’s air conditioners, trees support biodiversity (providing both habitat and food), improve mental health and assist in stormwater management.
Canopies slow the rate of precipitation, allowing rain to fall to the ground at a rate that can be absorbed by the soil, preventing sediment run-off into storm sewers and nearby waterbodies. This is a critical service in Calgary, where our volatile storms often overwhelm existing infrastructure.
As a part of natural infrastructure, trees are so effective that the City of Calgary has a valuation formula to assign a dollar value to public trees. This interactive map beautifully quantifies this data and allows anyone to learn more about the trees in their neighbourhood.
Same tree quantified by map
Calgary’s Urban Canopy
Calgary’s Urban Canopy is currently 8.25% and Calgary Parks has a mandate to increase coverage to 16% by 2060. By contrast, Vancouver’s canopy is estimated at 27% and Toronto’s is a whopping 33%.
Unlike Vancouver and Toronto, Calgary is not naturally hospitable to trees. It is arid and dry, prone to extreme temperature swings, and there are very few places within city limits where trees grow naturally. And while naturally occurring grasses, plants and wetlands provide many of the same benefits, trees that are able to withstand and thrive in these conditions must be prioritized as part of a comprehensive strategy for living with climate change.
Challenge: Private Lands
Planting new trees is an obvious part of the equation but in order to see the benefits provided by a healthy canopy right now, we need established trees.
Many trees within our urban canopy sit on private lands and therefore, cannot be actively protected. Awareness and education can reduce the likelihood of established trees being considered an inconvenience or nuisance and removed by private landowners.
Maintaining these established trees is also critical. Keeping trees healthy, free from disease, and resilient will help ensure a canopy that can withstand extreme weather events.
In order to reach the target of 16% canopy by 2060, Calgary needs to plant an additional 7,500 trees a year. Edmonton, a more hospitable tree climate, aims to plant 45,000 new trees annually.
In 2019, the City cut the budget for new trees (until 2022), choosing to spend only on pruning and maintenance of existing trees.
How Can You Help Our Urban Canopy?
Maintain: If you have trees on your property, maintain them. Both the City and the Calgary Horticultural Society have programming and resources designed around pruning, pest control and other interventions.
Plant: Maybe you are looking to add a tree or shrub to your property. The City has a helpful guide for recommending trees that are proven to thrive in our climate. Buying a tree from a local nursery will also help ensure that the trees have been appropriately hardened.
Advocate: Remind your councillors of the 2060 commitment frequently. If your community association has a green space it manages (like a garden), suggest a couple of trees be added. If you see a new development going up in your area and notice there are trees on the lot, contact the developer and ask what their plans are for retaining those trees.
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